The present invention relates to a pneumatic tire more particularly to a structure of the bead portion and lower sidewall portion being capable of improving the durability.
In Japanese patent Nos.2837840 and 2863510, the present inventor disclosed pneumatic tires improved in bead durability. In such tires, in order to reduce the tire weight as shown in FIG. 12, the carcass is composed of a single ply (c) having a toroidal main portion (c1) extending between a pair of bead portions and a turnup portion (c2) turned up around each bead core (b) from the axially inside to the outside of the tire. And the axial outer surface (d) of the bead portion is concavely curved. As the rubber between the carcass ply turnup portion (c2) and the outer surface (d) of the tire is relatively thin by nature, it is difficult to maintain the necessary rubber thickness (f) at the radially outer end (k) of the turnup portion (c2). If the thickness (f) is too small, stress during running concentrates on the outer end (k) and a separation failure liable to start from this outer end (k). Thus, in manufacturing such tires, the yield tends to lower.
It is therefore, an object of the present invention to provide a pneumatic tire, in which the necessary rubber thickness (f) is easily maintained without lowering the yield.
According to the present invention, a pneumatic tire comprises
a tread portion,
a pair of sidewall portions,
a pair of bead portions each with a bead core therein,
a carcass ply of cords extending between the bead portions through a tread portion and sidewall portions and turned up around the bead core in each bead portion from the axially inside to the outside of the tire to form a pair of turnup portions and a main portion therebetween,
a radially outwardly tapering rubber bead apex disposed between each of the turnup portions and the main portion,
in a meridian section of the tire, the sidewall portion and bead portion on each side of the tire having a profile comprising a first linear portion and a second linear portion each being substantially straight,
the first linear portion extending radially outwards from a point P in substantially parallel to the tire equatorial plane,
the second linear portion extending radially inwards from the point P while inclining axially inwards at an angle of from +15 to +60 degrees with respect to the tire equatorial plane,
each turnup portion extending radially outwardly beyond a radially outer end of the bead apex to form an adjoining part in which carcass cords in the turnup portion adjoin carcass cords in the main portion,
a radially outer end of the turnup portion disposed at a radial distance from a point Q which is in a range of less than 3 times a distance (gt) wherein the distance (gt) is defined as measured from the point P to the carcass ply main portion along a straight line drawn from the point P perpendicularly to the carcass ply main portion, and the point Q is defined as a point at which the straight line intersects the carcass ply main portion.
A standard inflated condition means that the tire is mounted on a standard wheel rim and inflated to a standard pressure but loaded with no tire load.
The standard wheel rim means the xe2x80x9cstandard rimxe2x80x9d specified in JATMA, the xe2x80x9cMeasuring Rimxe2x80x9d in ETRTO, the xe2x80x9cDesign Rimxe2x80x9d in TRA or the like. The standard pressure means the xe2x80x9cmaximum air pressurexe2x80x9d in JATMA, the xe2x80x9cInflation Pressurexe2x80x9d in ETRTO, the maximum pressure given in the xe2x80x9cTire Load Limits at Various Cold Inflation Pressuresxe2x80x9d table in TRA or the like. In case of passenger car tires, however, 180 kPa is used as the standard pressure.
A standard load means the xe2x80x9cmaximum load capacityxe2x80x9d in JATMA, the xe2x80x9cLoad Capacityxe2x80x9d in ETRTO, the maximum value given in the above-mentioned table in TRA or the like.
A tire section height means the radial distance of the radially outermost point of the tread portion measured from a bead base line under the standard inflated condition.
The bead base line is an axial line drawn at the diameter of the wheel rim.
A maximum tire width point means a point on the outer surface of each sidewall portion at which the cross sectional width of the tire is maximum under the standard inflated condition. In case a part having a certain radial extent shows the maximum cross sectional width, the maximum tire width point is defined by the radially outer end of such part.
A standard free condition means that the tire is not mounted on a wheel rim and held vertically, and measurements under this condition mean those of the uppermost part of the tire.